With the advent of more and more powerful computers, it has become increasingly important to have available large capacities of data storage for use in conjunction with such computers. The prevailing technologies for such storage, typically referred to as "secondary storage" include magnetic tape and rotating disks. Rotating disks include "rigid" or "hard" disks, also known as "Winchester" disks.
Rigid disks include an extremely smooth circular platter fabricated of aluminum or other suitable material. The platter is typically coated with a thin magnetic film or coating. Binary data is stored on the magnetic medium via electro magnetic or magneto optic techniques well known in the art. Alternatively, binary data is stored on a layer via known optical recording techniques. Such techniques are described in an article entitled "Data-Storage Technologies for Advanced Computing" appearing in the October 1987 issue of Scientific American.
Traditional hard disks suffer from operational characteristics which adversely effect the storage capacity of the device, the useability of the disk in environments subject to mechanical shock and vibration, and in thin atmosphere such as encountered at high elevations and in space.
To date, efforts to increase the recording density on hard disks have included changes in the head design to increase the linear bit density, reduction in the width of the head to reduce the track widths thereby permitting greater track densities and via the use of thinner layers of magnetic media.
While it has been recognized that positioning the head closer to the medium, i.e. reducing the flying height, would permit greater recording densities, it has been generally believed that reducing the flying height would be extremely difficult in practice (see Scientific American, October 1987, Page 120).
The difficulties associated with increasing the recording density by reducing the flying height are in part a consequence of the mechanism employed to establish the flying height in rigid disk drives. Heads in rigid disk drives typically ride on an "air bearing" which cause the head to be supported on a cushion of air approximately six to twelve micro-inches above the surface of the rotating disk. The flying height is a function of the relative velocity between the head and the rotating disk. The velocity of the head with respect to the disk at any given concentric track radius on the disk is equal to the circumference of the disk at the given track times the speed of revolution of the disk. Since the relative velocity of the head with respect to the disk is directly proportional to the radius, and since the flying height is a function of the relative velocity between the head and the disk, the flying height at the outside diameter of the disk is considerably greater then the flying height at the inside diameter of the disk. As a consequence of the fact that the flying height increases as a function of radius in conventional hard disk systems with a corresponding decrease in linear bit recording densities, the recording capacities achieved in such systems are greatly reduced.
Another disadvantage associated with the use of air bearing as the primary means of supporting the head is that upon removal of power (power down), the head "lands" on the media and upon application of power (power up), the head contacts the media during "take-offs" resulting in head wear and abrasion of the media. To address the problem of media abrasion and corruption of data in conventional hard disk systems, a landing zone is often provided which is devoid of recorded data. While this approach prevents the loss of recorded data, it does not address the problems associated with signal degradation due to head wear occurring during take offs and landings.